Final Fantasy Advance and Chrono Trigger DS Font Specifications
By Dragonsbrethren
Revision 1.2
------------------------------------------------------------------------------
INTRODUCTION
***********************
  Final Fantasy IV, V, and VI Advance, and Chrono Trigger DS all store their
fonts in the same format. The actual pixel data is stored in the same two
bits-per-pixel (2BPP) format that Virtual Boy games use, which is commonly
called VB format in tile editors. The properties of the fonts themselves are
determined by a header in the "font table," which also contains pointers to
each character. The width information for each character is stored before the
character itself.
------------------------------------------------------------------------------
FONT TABLES
***********************
  All font tables begin with an twelve byte header:
  
  00: Unknown, always $00.
  01: Unknown, always $00.
  02: Unknown, always $00.
  03: Unknown, always $00.
  04: $46 (F)
  05: $4F (O)
  06: $4E (N)
  07: $54 (T)
  08: The height of every character in the font, in pixels.
  09: Bit depth (always $02).
  10: Number of characters in font (low byte).
  11: Number of characters in font (high byte).

  These are followed by 256 ($FF) bytes of unknown purpose. Next up is a table
of 32-bit pointers, one per character, which are used to determine where the
header for each character begins. These pointers are relative to the offset of
the font table, meaning it is not possible for characters to precede the table.
The pointer table is not terminated by anything other than the number of
characters in the font. In the unmodified games, the characters themselves
directly follow each pointer table, but this is not a requirement.
------------------------------------------------------------------------------
CHARACTER HEADERS AND PIXEL DATA
***********************
  Each character has a two byte header:
  
  00: Character width, in pixels.
  01: Character width, in columns.

  The first byte only determines when the game will start drawing the next
character in a string. For example, if your character is six pixels wide, but
you change this to $04, two pixels will overlap the next character.

  The columns are much more important, and determine how wide the character
actually is. One column is four pixels wide, two columns are eight, three
are twelve, etc.

  After the header is the pixel information itself. This 2BPP format stores
four pixels per byte; these pixels make up one line of a column. The number of
lines needed for each character is determined by the height of the font. For
characters with multiple columns, the bytes are interlaced. This means that
the first byte is the first line of column one, the second byte is the first
line of column two, etc. for each column. This also means that the number of
bytes required for a character is equal to the height of the font times the
number of columns.

Which bits are toggled determines the color of the pixel:

  00: Transparent
  01: White
  10: Black
  11: Gray

  Characters aren't terminated by anything, the game simply doesn't render
any bytes past the ones required by the character. The pointers determine
where each character begins; for maximum efficiency every character is
directly followed by the next in the stock font tables.
------------------------------------------------------------------------------
EDITING
***********************
  There is now a utility, created by HoRRoR, which can edit these fonts:
  
  http://www.romhacking.net/utils/624/
  
  In order to use it, dump the entire font table to a binary file with a .fnt
file extension. You can then adjust the character widths, remove characters
from the font, and export/import single characters to/from bitmaps. The
utility also works with the fonts in Final Fantasy I & II: Dawn of Souls,
which this document does not cover.
------------------------------------------------------------------------------
CONTACT INFORMATION
***********************
  Please email any additions or corrections to the following address:
  
  dragonsbrethren-at-gmail.com
------------------------------------------------------------------------------
2009 Dragonsbrethren Industries